The study's long-term objective is to advance understanding of the etiologic role of pre- and perinatal complications in Bipolar Disorder. If such complications are indeed etiologically significant, it could have important health implications, since improved obstetric care targeted on individuals at high risk for Bipolar Disorder would then offer an attractive approach to primary prevention. The specific aim is to investigate whether it is possible to confirm and extend, with a new and larger sample, and improved methodology, pilot study findings of an excess of obstetrical complications (OCs) in probands with Bipolar Disorder, compared to their own psychiatrically normal sibs. The research design and methods will involve obtaining medical records on the births and pregnancies of 60 subjects with Bipolar Disorder aged 25-35 and all available sibs of the same age, including at least 60 psychiatrically normal sibs. Diagnoses using DSM-III-R criteria will be made based on structured diagnostic interviews (SCID supplemented by additional questions on symptoms of mood disorders) and by a review of pertinent medical records. Summary OC scores, using published scales applied by several groups of investigators in previous studies of OCs and psychiatric disorders, will be obtained based on careful review of obstetrical records. A supplementary score will include OCs reported in interviews with probands' mothers. Ratings of OCs and psychiatric diagnoses will be made blind with respect to each other. A larger sample, composed of approximately 80 bipolar probands and their siblings, will be studied to insure that at least 60 sibships can be obtained with detailed obstetrical records on both the proband and at least one normal sibling, and that groups of probands and sibs are similar in mean age, birth order, and sex. Sample sizes have been chosen to provide good statistical power, based on a power analysis using effect sizes similar to those found in our pilot study. Nonparametric statistical procedures will be used on our ordinal OC score data to test the hypothesis that bipolar probands have significantly higher OC scores than their normal sibs. Exploratory analyses will examine related questions, such as whether specific types of OCs are most strongly associated with Bipolar Disorder.